Seven-membered rings, synthesis

Scheme 13.5 Representative thermal cycloadditions for seven-membered ring synthesis.

The Baeyer-Villiger oxidation of cyclohexanone to form e-caprolactone (78) using peroxybenzoic acid, as indicated in equation (40), may be considered as a further type of intramolecular displacement reaction of value in seven-membered ring synthesis (49JA2571). 

Lewis acid mediated intramolecular C-C bond formations represent another major class of reactions adaptable to seven-membered ring synthesis. A superb example of this class is found in the work of Majetich, which features a titanium-induced cyclization reaction employed in the synthesis of several natural products, including bar-batusol (Eq. 4)7 Although technically this closure has a nucleophilic... 

V. CYCLOADDITION STRATEGIES FOR SEVEN-MEMBERED RING SYNTHESIS... 

Figure 2. Cycloaddition approaches to seven-membered ring synthesis that are isoelectronic with the Diels-Alder reaction.

As an extension of his studies in the field of the skeletal rearrangement and cycloaddition involving carbon monoxide, Wender reported a new method for seven-membered ring synthesis through a carbonylative ring-expansion reaction of allenylcyclobutanes as a formal [6-H] cycloaddition (Scheme 8.12) [27]. The reaction is believed to proceed through the formation of rhodacycloheptene followed by CO insertion and reductive elimination of the metal species. 

Wender, P. A., Deschamps, N. M., Sun, R. (2006). Rh(I)-catalyzed CC bond activation seven-membered ring synthesis by a [6-1-1] carbonylative ring-expansion reaction of allenylcyclobutanes. Angewandte Chemie, International Edition, 45, 3957-3960. 

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